1. Field of the Invention
The present invention relates to a robot control system and, more particularly, relates to a robot control system having an inexpensive, high safety servo power connection/cutoff circuit utilizing software.
2. Description of the Related Art
A servo amplifier of a robot control system is provided with an AC/DC converter. In such a servo amplifier, when the power is turned on, a large rush current would flow through a smoothing capacitor in the servo amplifier (hereinafter simply referred to as a “capacitor”), so the robot control system is provided with a precharging circuit.
At the time of startup of the servo amplifier, to enable a charging resistance in the precharging circuit (hereinafter simply referred to as the “resistance”) and a serial contact (relay or solenoid switch) to perform the precharging at the time of startup, then connect to the main power source, a main circuit contact is provided parallel to the serial line between the resistance and serial contact, the contact in series with the resistance is closed to start the precharging, the capacitor is charged, then the main circuit contact is closed.
On the other hand, when cutting the servo power at the time of an emergency stop, both the precharging contact and the main circuit contact are opened, but for safety's sake, it is necessary to detect faults such as melt fusion of the contacts.
In the related art, for example, in the emergency stop circuit described in Japanese Patent Publication (A) No. 2004-237416 (see specification, paragraph nos. [0023] to [0037] and drawings, FIGS. 3 and 4) or Japanese Patent Publication (A) No. 2005-165755 (see claims, [Claim 1], specification, paragraph nos. [0023] to [0037], and drawings, FIGS. 1 and 2), the function of detecting melt fusion faults of contacts was realized by using hardware circuits, but the circuits were complicated and the costs high.
FIG. 1 is a general electrical system diagram of the robot 1 and the robot control system 2. The controller 11 shown in FIG. 1 includes a CPU for controlling the robot operation and its peripheral circuits and enables the robot 1 to perform predetermined work by issuing commands to the servo amplifier 12 to control the robot 1 in operation and posture.
Further, the controller 11 has a teaching pendant 13 connected to it. The teaching pendant 13 is operated by a worker to teach the robot 1 an operation or to input various settings into the robot control system 2.
The servo amplifier 12 drives a servo motor attached to each joint of the robot 1 based on a command from the controller 11. Further, the servo amplifier 12 receives feedback information relating to the rotational angle and speed from a rotary encoder attached to each servo motor through a signal line 15 and transmits information necessary for control of these servo motors to the controller 11.
The servo power connection/cutoff circuit 14 turns on the drive power for the servo motors of the robot 1 through the servo amplifier 12 and power line 16 in accordance with a request for startup of the robot 1 or immediately cuts the supply of drive power to the servo motors to ensure safety when there is a request for emergency stop.
FIG. 2 is a block diagram of the configuration of the servo amplifier 12 shown in FIG. 1. The servo amplifier 12 has an AC/DC converter 21 for converting a drive power, that is, an AC power, to a DC power and an inverter 22 for converting a DC power to an AC power controlled in current by a command from the controller 11. Further, to smooth the output voltage of the AC/DC converter 21, a large capacity smoothing capacitor 23 is provided. The inverter 22 receives as input the DC voltage smoothed by the capacitor 23.
When connecting the servo power to the servo amplifier 12, if directly applying the power voltage in the state with the capacitor 23 insufficiently charged, a large rush current would flow into the capacitor 23 and the electrical circuits in the current path would be adversely affected or a temporary voltage drop would be caused, so before connecting the power source, the general practice has been to precharge the capacitor 23 through a resistance.
FIG. 3 is a view of details of the servo power connection/cutoff circuit 14 shown in FIG. 1, while FIG. 4 is a view showing the change in state of the servo power connection/cutoff circuit 14 shown in FIG. 3. The servo power connection/cutoff circuit 14 shown in FIG. 3 has the function of cutting the supply of drive power to the servo amplifier 12 (hereinafter referred to as the “servo power”) when the operator pushes the emergency stop switch 31 and the function of connecting the servo power when the operator releases the emergency stop switch 31 and pushes the reset switch 32.
Further, when connecting the servo power, it has the function of precharging to prevent a large rush current from flowing to the servo amplifier 12.
Below, details of the servo power connection/cutoff circuit 14 will be explained. In FIG. 3 and FIG. 4, KA1, KA2, and KA3 indicate relays, while KM1 and KM2 indicate electromagnetic contactors. The relays and electromagnetic contactors used are ones for which linkage between normally open contacts and normally closed contacts is ensured (interlocked).
For example, when the contact KM1-1 of the KM1 is closed, the normally open contacts KM1-4 to KM1-6 being in the open state is guaranteed.
First, these relays (KA1 to KA3) and electromagnetic contactors (KM1, KM2) are all in the OFF state (state of S0 of FIG. 4).
At this time, if the relays and electromagnetic contactors are free of faults such as melt fusion or reset defects of the normally open contacts and the normally open contacts open, the contacts KA2-2, KM1-1, KA3-2, and M2-1 become closed.
If the operator pushes the reset switch 32 in this state, the KA1 enters the ON state and the KA1-1 and KA1-2 close (state of S1 of FIG. 4). At this time, if the emergency stop signal switch 31 is in the closed state, the KA2 and KA3 turn ON through these contacts (state of S2 of FIG. 4). Note that if the emergency stop switch 32 is in the opened state, KA2 and KA3 will never turn ON.
If the KA2 and KA3 turn ON, the KA2-2 and KA3-2 are opened, so the KA1 enters the OFF state, but current flows through the KA2-1 and KA3-1, so while the emergency stop switch 31 is in the closed state, the ON states of KA2 and KA3 are held (state of S3 of FIG. 4). Therefore, the operation of pushing the reset switch 32 may be short in time.
When the KA2 becomes ON and the KA1 becomes OFF, the KM1-3 and the KM2-3 become closed and the KM1 is ON. At this time, the KM1-4 to KM1-6 and the KA3-4 to KA3-6 are in the closed state and the KA3 is ON, so the capacitor 23 in the servo amplifier 12 is charged through the KA3-4 to KA3-6 and charging resistance 35. The current at this time is limited by the charging resistance 35, so a large rush current will not flow.
The power-up delay circuit 36 is set so as to turn ON the KM2 through the KA1-3 to KA3-3 after the time for the capacitor 23 in the servo amplifier 12 to be sufficiently charged elapses from the time when the KA3 turns ON. Due to this, the rush current is prevented from flowing when the KM2-4 to KM2-6 are ON.
In the above way, finally, only the KA1 enters the OFF state while the other KA2, KA3, KM1, and KM2 all become the ON state, whereby the preparations for operation end (state of S4 of FIG. 4).
When the button of the emergency stop switch 31 is pushed, all of the relays (KA1 to KA3) and electromagnetic contactors (KM1, KM2) turn OFF and the initial state (state of S0 of FIG. 4) is returned to.
In the event that in the relays or electromagnetic contactors forming the servo power connection/delay circuit 14, the normally open contacts melt fuse or other reasons occur in the initial state (S0) and the normally open contacts can no longer be reset, the contacts corresponding to the faulty parts in the KA2-2, KM1-1, KA3-2, and M2-1 will not become the closed state. Therefore, the change from S0 to S1 will not occur and the servo amplifier will not enter a state where it is supplied with power, that is, the state of S3 and S4 will not be reached. Therefore, the operator will notice the fault and servo power will not longer be supplied in the faulty state, so safety will be secured.
Due to the above power connection/cutoff circuit, safety against a fault in the power connection/cutoff circuit can be secured. Due to the precharging, the rush current to the servo amplifier can be suppressed. Due to the increased complexity of the circuit and the increase in the number of parts, an increase in cost cannot be avoided. Further, relays where linkage between the normally open and normally closed contacts is guaranteed are extremely expensive compared with general relays. This also is a factor to increase costs.
Before turning the servo power ON, it is possible to detect faults in the power connection/cutoff circuit, but once turning the power ON, there is the problem that a fault cannot be detected while ON.